Yep, it does make a kind of sense since while games like minecraft have helped show people that games are often ugly and for a long time, there's still plenty of people that'll get in at alpha stage and whinge about it not being complete. So you gate it so that only those that really want that early access get it.
Ah, a reverse Minecraft!
It's a(nother) spiritual successor to Total Annihilation and it's Ł68 because they had a tiered rollout they planned with their kickstarter. So while it's in alpha at the moment it costs the most to get in, beta will be less and finally retail will be a normal amount.